At present, a transmission opportunity (TXOP, transmission opportunity) mechanism is supported in a wireless local area network, where when obtaining a transmission opportunity, a station (STA, station) may reserve a period of time during which one or multiple data frames may be transmitted continuously. The station obtaining the transmission opportunity is called a transmission opportunity holder (TXOP holder). A NAV (network allocation vector, network allocation vector) is set at a station of a receiver of data sent by a non-transmission opportunity holder, so as to ensure that the non-transmission opportunity holder does not contend within a time range reserved by the transmission opportunity holder.
However, in a specific application, a problem of asymmetrical uplink and downlink data traffic usually occurs in the wireless local area network, that is, data traffic in one link direction is far heavier than that in the other link direction. In order to solve the problem, a reverse direction protocol (reverse direction protocol, RD) mechanism is supported in a current standard, which refers to that: When a station (assumed to be STA-a) obtains, by contending, a transmission opportunity (TXOP) of a certain time length, if there is remaining time after the station finishes sending data to another station (assumed to be STA-b), it may grant a right to use a channel to STA-b; and STA-b sends data to STA-a by using the remaining TXOP time, and returns the transmission opportunity to STA-a after finishing the sending. STA-a is called a reverse direction protocol RD initiator, while STA-b is called a reverse direction protocol RD responder.
With the development of technologies, a multi-user transmission (for example: Multi-Users Multi-input and Multi-output, MU-MIMO) technology is introduced, that is, a station simultaneously sends data to two or more than two stations in a same frequency band. In the MU-MIMO technology, orthogonality of channels between users is mainly utilized, channel utilization is improved, and system throughput is increased. However, a current reverse direction protocol mechanism cannot transmit MU-MIMO data. Therefore, a capability of an access point AP for sending the MU-MIMO data is limited, the channel utilization is reduced, which is bad for improving the system throughput.